I think the engineers at Triumph have long known what we have learned. They have contraints we don't, mostly price points and government regs. Point in case, I doubt Triumph could get a factory installed T-Bird big bore into the country (USA). Plus it's easier to sell a $12500 Triumphs than a $15000 ones. Besides you can install the 100cc kit any time during ownership. For about $1500 plus 8 hours labor you get a 100 cubic inch T-Bird. I think it include air box mod, remap, pipes, and a 100 cubic inch clutch cover Triumph will only sell you if you've done the kit.
Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.
H. L. Mencken